Various substituted tetracyclic heterocyclic compounds are inhibitors of the HCV NS5A enzyme. Included in these heterocycles are those related to Compound A, as defined and described below. These compounds and pharmaceutically acceptable salts thereof may be useful in the treatment or prophylaxis of infection by HCV and in the treatment, prophylaxis, or delay in the onset or progression of HCV infection. Representative tetracyclic heterocyclic compounds that may be useful for treating HCV infection are described, for example, in US Patent Publication No. US20120083483 and International Patent Publication Nos. WO14/110,705 and WO 2014/110,706. Among the compounds disclosed in WO14/110,705 is dimethyl ((2S,2′S)-((2S,2′S)-2,2′-(5,5′-((S)-6-(2-cyclopropylthiazol-5-yl)-1-fluoro-6H-benzo[5,6][1,3]oxazino[3,4-a]indole-3,10-diyl)bis(1H-imidazole-5,2-diyl))bis(pyrrolidine-2,1-diyl))bis(3-methyl-1-oxobutane-2,1-diyl))dicarbamate, hereinafter referred to as Compound A. Compound A is a known inhibitor of HCV NS5A. The structure of Compound A is as follows:

International Publication Number WO14/110,705 discloses methodology that can be used to prepare Compound A and related tetracyclic HCV NS5A inhibitors. This general methodology is illustrated immediately below:
The methods described in US Patent Publication No. US20120083483 and International Publication Numbers WO14/110,705 and WO14/110,706 are practical routes for the preparation of Compound A and related tetracyclic heterocyclic compounds. Nonetheless, there is always a need for alternative preparative routes which, for example, use reagents that are less expensive and/or easier to handle, consume smaller amounts of reagents, provide a higher yield of product, involve fewer steps, have smaller and/or more eco-friendly waste products, and/or provide a product of higher purity.
Unlike the disclosed methods for making tetracyclic HCV NS5A inhibitors described in US Patent Publication No. US20120083483 and International Publication Numbers WO14/110,705 and WO14/110,706 the process of the present invention employs fewer steps and provides an improved yield of Compound A and related NS5A inhibitors.